1. Field of the Invention
The present invention relates to an optical information recording medium and an optical information recording and reproducing apparatus for recording and reproducing information by using a light beam. More particularly, the present invention relates to an optical information recording medium and an optical information recording and reproducing apparatus allowing for obtaining a higher track density by recording a signal on both lands and grooves of the guide grooves thereof.
2. Description of the Related Art
Optical disks, optical cards, optical tapes and the like are well-known as recording mediums (or recording members) for recording and/or reproducing information by the use of an optical means. In order to record information on such a recording medium, a laser beam is generally used as a light source. More specifically, information is recorded by precisely focusing a light beam through a lens so as to irradiate the light beam on a recording thin film of the recording medium.
An optical disk, one of the above-cited recording media, includes a circular substrate on which spiral or concentric guide grooves having a plurality of convex portions and concave portions are provided, and a recording thin film formed thereon. By irradiating a light beam, which is intensity-modulated in accordance with each information signal, along the direction of these guide grooves, information is recorded on the recording thin film.
The recording thin film is required to exhibit such characteristics that the physical properties thereof are varied upon the irradiation of light, and that the difference between the states before and after the variation may be optically detected. The variations in the physical properties of the recording thin film, are for example, the deformation of the thin film owing to the absorption of the light, the phase change of the thin film owing to the light irradiation, and the like. The recording media showing such variations are known as a deformation type recording medium and phase-change type recording medium, respectively. A signal indicating the variations of the physical properties as difference in the amounts of the reflected light is reproduced.
A magnetooptic recording medium is also well-known as another optical type recording medium. In a magnetooptic recording medium, information is recorded thereon by the application of a magnetic field as well as light irradiation, and the difference in the magnetization directions on the recording thin film is detected by utilizing a Kerr effect, thereby reproducing a signal.
Optical type recording media such as those described above have been put into practical use depending on the respective applications thereof. In addition, in order to further increase the memory capacity for information, various kinds of researches on the increase of the recording density have been earnestly conducted.
As an exemplary method for increasing the recording density of an optical type recording medium, a method for recording a signal both on the convex portions and concave portions of the guide grooves is proposed so as to replace a conventional method for recording a signal on either the convex portions or the concave portions of the guide grooves (e.g., Japanese Journal of Applied Physics, Vol. 32 (1993), pp. 5324-5328). According to the method disclosed therein, by using a substrate in which the width of a concave portion of each guide groove is approximately equal to that of a convex portion thereof, and the depth of the concave portion is optimized, an information signal may be recorded and reproduced on/from both of the concave portion and the convex portion. In this specification, a convex portion with respect to the light incident direction is called a xe2x80x9cgroovexe2x80x9d, and the operation of recording information on a convex portion is called a xe2x80x9cgroove recordingxe2x80x9d. In the same way, a concave portion with respect to the light incident direction is called a xe2x80x9clandxe2x80x9d, and the operation of recording information on a concave portion is called a xe2x80x9cland recordingxe2x80x9d. If a method for recording a signal on both of lands and grooves is employed, a track density is considered to become double as compared with a conventional method in which information is recorded on either one side of each guide groove.
In recording and reproducing information in accordance with this method, the same kinds of optical systems and optical type recording systems as conventional ones may be used in principle. This method may be realized easily by additionally providing a tracking polarity switching means so as to correspond to each concave portion and each convex portion of the guide grooves, and by irradiating an intensity-modulated light beam on the two kinds of regions based on the information signals. However, the comparison of the two kinds of signals recorded on the two kinds of portions of the recording medium reveals that difference exists in the amplitude and the frequency characteristics of the two kinds of reproduced signals corresponding to a land and a groove, respectively. Such difference in the amplitude of the signals is also caused depending on the configuration of the respective recording thin films. Therefore, even if a signal recording may be satisfactorily performed on either one of a land track and a groove track during a step of demodulating a reproduced signal, a great deal of error is generated on the other kind of track in some cases. Also, even in recording thin films having the same configuration, if the shape of the edges of the guide grooves or the groove width become different from each other, the levels of the reproduced signals become different on the two kinds of tracks.
Accordingly, in a conventional recording medium for performing a land/groove recording, there exists problems to be solved in that the configuration of a recording thin film is required to be optimized and that the guide grooves on the substrate must be shaped with high precision.
An optical information recording and reproducing apparatus for recording and reproducing an information signal on/from both concave portions and convex portions of guide grooves formed on a recording medium is provided. The recording medium has: a substrate on which the guide grooves consisting of the concave portions and the convex portions are formed; and a recording thin film, formed on the guide grooves, on which variations to be detected optically are generated by irradiation of light is provided. The optical information recording and reproducing apparatus of the invention includes: an optical portion, having a light source, for focusing a light beam emitted from the light source on the recording medium using an objective lens; a focusing control portion for controlling so as to make a focal point of the light beam correspond to a position of the recording thin film; a tracking control portion for controlling a position of the light beam in a direction substantially vertical to the guide grooves so that the light beam tracks the guide grooves; a selection portion for selecting which of the concave portions and the convex portions of the guide grooves are used for recording a information signal thereon or reproducing a recorded information signal therefrom; a polarity inverting portion for inverting the polarity of an output signal from the tracking control portion depending on a result selected by the selection portion; a waveform setting portion for setting a modulation pattern for the light beam to be irradiated on the recording medium in accordance with the information signal; and a signal reproduction portion for demodulating the information signal from a light reflected or transmitted by recorded marks recorded on the recording medium; wherein at least one of the focusing control portion, the tracking control portion, the waveform setting portion and the signal reproduction portion has at least two kinds of operation conditions for recording and reproducing the information signal on/from the concave portions and the convex portions of the guide grooves, and wherein the operation conditions are selected depending on the result selected by the selection portion.
According to another aspect of the invention, an optical information recording and reproducing apparatus includes: an optical portion, having a light source, for focusing a light beam emitted from the light source on the recording medium using an objective lens; a focusing control portion for controlling so as to make a focal point of the light beam correspond to a position of the recording thin film; a tracking control portion for controlling the position of the light beam in a direction substantially vertical to the guide grooves so that the light beam tracks the guide grooves; a selection portion for selecting which of the concave portions and the convex portions of the guide grooves are used for recording the information signal thereon or reproducing a recorded information signal therefrom; a polarity inverting portion for inverting the polarity of an output signal from the tracking control portion depending on a result selected by the selection portion; and an optical modulation portion including a waveform setting portion having at least two kinds of modulation patterns in accordance with the information signal in order to record the information signal on each of the concave portions and the convex portions of the guide grooves so as to output any of the modulation patterns depending on the result selected by the selection portion, wherein the optical modulation portion modulates an intensity of the light beam in accordance with the modulation patterns output from the waveform setting portion.
In one embodiment of the invention, the waveform setting portion has a multiple pulse modulation function for irradiating a light consisting of a plurality of pulse sequences onto one recorded mark to be recorded on the recording medium, and wherein waveforms of the plurality of pulse sequences are different from each other among the at least two kinds of modulation patterns of the waveform setting portion.
In one embodiment of the invention, the said at least two kinds of modulation patterns of the waveform setting portion vary the power of the light beam.
In one embodiment of the invention, the recording and reproducing apparatus further includes a signal reproduction portion for demodulating the information signal from a light reflected or transmitted by recorded marks recorded on the recording medium, wherein before recording the information signal on the recording medium, the waveform setting portion includes a recording condition setting portion in which a plurality of pulse patterns are stored in order to irradiate the light beam having different modulation patterns onto the concave portions and/or the convex portions of the guide grooves in a test zone close to an information zone on the recording medium; and wherein a plurality of recorded marks are formed on the recording medium by irradiating the light beam modulated by the optical modulation portion in accordance with the plurality of pulse patterns, information signals to be obtained from the plurality of recorded marks formed on the recording medium are demodulated by the signal reproduction portion, and qualities of a plurality of reproduced signals obtained by the signal reproduction portion are compared with each other, thereby determining recording conditions optimized for the concave portions and the convex portions of the guide grooves.
In one embodiment of the invention, the recording and reproducing apparatus further includes a recording condition identifying portion for reading a recording condition identifier, provided in a particular zone other than the information zone on the recording medium, for correcting a difference between characteristics of the concave portions and those of the convex portions of the guide grooves, wherein the wave form setting portion is operated depending on information read by the recording condition identifying portion.
According to still another aspect of the invention, an optical information recording and reproducing apparatus includes: a selection portion for selecting which of the concave portions and the convex portions of the guide grooves are used for recording the information signal thereon or reproducing a recorded information signal therefrom; an optical portion, having a light source, for focusing a light beam emitted from the light source on the recording medium using an objective lens; a focusing control portion, including an offset setting portion for supplying offsets having at least two levels to the concave portions and the convex portions of the guide grooves, for controlling so as to make a focal point of the light beam correspond to a position of the recording thin film by using the offsets selected depending on a result selected by the selection portion; a tracking control portion for controlling the position of the light beam in a direction substantially vertical to the guide grooves so that the light beam tracks the guide grooves; and a polarity inverting portion for inverting the polarity of an output signal from the tracking control portion depending on the result selected by the selection portion.
In one embodiment of the invention, the recording and reproducing apparatus further includes a signal reproduction portion for demodulating an information signal from a light reflected or transmitted by recorded marks recorded on the recording medium, wherein the focusing control portion includes a focusing condition setting portion in which a plurality of offset levels for recording and reproducing the information signal are stored, and wherein before recording and reproducing the information signal on/from the recording medium, a plurality of recorded marks are formed in a test zone close to an information zone on the recording medium by irradiating the light beam onto the concave portions and/or the convex portions of the guide grooves using the plurality of offset levels, a plurality of reproduced signals to be obtained from the plurality of recorded marks formed on the recording medium are demodulated by the signal reproduction portion using the light beam, and qualities of the plurality of reproduced signals obtained by the signal reproduction portion are compared with each other, thereby determining recording conditions optimized for the concave portions and the convex portions of the guide grooves.
In one embodiment of the invention, the recording and reproducing apparatus further includes a signal reproduction portion for demodulating an information signal from a light reflected or transmitted by recorded marks on the recording medium, wherein the focusing control portion includes a focusing condition setting portion in which a plurality of offset levels for recording and reproducing the information signal are stored, and wherein before recording or reproducing the information signal on/from the recording medium, information signals to be obtained from reference recorded marks formed in a test zone close to an information zone on the recording medium are demodulated by the signal reproduction portion using the light beam with the plurality of offset levels, and qualities of a plurality of reproduced signals obtained by the signal reproduction portion are compared with each other, thereby determining reproducing conditions optimized for the concave portions and the convex portions of the guide grooves.
In one embodiment of the invention, the recording and reproducing apparatus further includes a jumping portion for moving the light beam by a half track from a concave portion of the recording medium to a convex portion adjacent to the concave portion, or from a convex portion to a concave portion in association with an operation of the polarity inverting portion, wherein an offset at a level between a level of an offset of the focusing control portion with respect to the concave portions of the recording medium and a level of an offset of the focusing control portion with respect to the convex portions of the recording medium is used during an operation of the jumping portion.
In one embodiment of the invention, the tracking control portion comprises a second offset setting portion for supplying at least two offset levels, and wherein the offset levels of the second offset setting portion are switched depending on a result selected by the selection portion.
According to still another aspect of the invention, an optical information recording and reproducing apparatus includes: an optical portion, having a light source, for focusing a light beam emitted from the light source on the recording medium using an objective lens; a focusing control portion for controlling so as to make a focal point of the light beam correspond to a position of the recording thin film; a tracking control portion for controlling a position of the light beam in a direction substantially vertical to the guide grooves so that the light beam tracks the guide grooves; a selection portion for selecting which of the concave portions and the convex portions of the guide grooves are used for recording the information signal thereon or reproducing a recorded information signal therefrom; a polarity inverting portion for inverting the polarity of an output signal from the tracking control portion depending on the result selected by the selection portion; and a signal reproduction portion for demodulating the information signal from a light reflected or transmitted by recorded marks recorded on the recording medium in the concave portions and the convex portions of the guide grooves by switching at least two demodulation conditions depending on the result selected by the selection portion.
In one embodiment of the invention, the mentioned at least two demodulation conditions are equalizing conditions having different amplification characteristics with respect to a frequency.
In one embodiment of the invention, the signal reproduction portion includes at least two level setters for generating reference signals at different levels and a comparator for comparing the information signal from the recording medium with one of the reference signals, and wherein the said at least two demodulation conditions are the reference signals for binary coding.
In one embodiment of the invention, before demodulating the information signal from the recording medium, signals to be obtained from reference recorded marks formed in the concave portions and the convex portions of the guide grooves in a test zone close to an information zone on the recording medium are reproduced; the signals are demodulated by gradually varying demodulation conditions of the signal reproduction portion; and then the demodulated signals are compared with each other, thereby determining optimal demodulation conditions.
According to still another aspect of the invention, an optical information recording medium includes: a substrate having guide grooves consisting of concave portions and convex portions thereon; a recording thin film, provided on the substrate, on which variations to be detected optically are generated by irradiation of light; and land/groove identifiers, provided in a particular zone other than an information zone on the recording thin film, for indicating differences between characteristics of the concave portions and those of the convex portions of the guide grooves.
In one embodiment of the invention, the land/groove identifiers include information indicating irradiation conditions of light during a recording operation.
In one embodiment of the invention, the land/groove identifiers include identifiers consisting of information about groove shapes of the concave portions and the convex portions of the guide grooves.
In one embodiment of the invention, the land/groove identifiers are reference record signals, provided on the concave portions and the convex portions of the guide grooves in a test zone close to an information zone on the same plane of the recording medium, for determining reproduction conditions of the information signal recorded in the information zone.
According to the present invention, the recording conditions are varied depending on which of the concave portions and the convex portions of the guide grooves are tracked, so that a recording may be performed while compensating for the difference between the heating/cooling characteristics of the grooves and those of the lands, whereby information may be recorded stably.
In addition, any focusing errors and tracking errors which are caused during tracking the concave portions and convex portions of the guide grooves and the distortion of the reproduced signal to be generated during the signal demodulation may be compensated for independently.
Thus, the invention described herein makes possible the advantage of providing an optical information recording medium and an optical information recording and reproducing apparatus in which reading errors may be reduced both on the lands and the grooves of the guide grooves.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.